The present invention relates generally to knee orthoses, and more particularly to a knee orthosis which causes the patella to properly track the trochlear groove during movement of the knee.
The patello-femoral joint of the knee is an articulation between the patella and femur. The joint consists of an articular surface on the posterior of the patella and a corresponding articular surface on the anterior of the head of the femur which is termed the trochlea. The posterior of the patella is contoured as a ridge, while the trochlea is contoured as a groove which is dimensioned to receive the patellar ridge in a complementary manner. Proper dynamic function of the patello-femoral joint requires that the patellar ridge accurately track the underlying trochlear groove when the knee is moved through flexion or extension. The anatomy and function of the patello-femoral joint are well known and described in detail in Ficat, R. P. et al., Disorders of the Patello-femoral Joint, Williams and Wilkins, 1977.
Functional disorders of the patello-femoral joint frequently relate to improper dynamics. Less severe forms of patello-femoral joint disorder cause pain in the joint, but do not exhibit errors in patellar tracking of the trochlear groove. In more severe forms of patello-femoral joint disorder, patellar tracking errors are evident in addition to joint pain, but there is no subluxation or dislocation of the joint. In still more severe forms of patello-femoral joint disorder, patellar tracking errors result in subluxation or dislocation of the joint. Recurrent subluxation of the patello-femoral joint is a particular disorder whereby the patella deviates transiently and typically rapidly from its normal axis of movement due to patellar tracking errors during movement of the knee. Slight deviations of the-patella from its normal axis of movement are termed minor subluxation and may not produce any clinically apparent relocation of the patella. Minor subluxation is often the result of a functional imbalance in the knee. Significant deviations of patellar movement which approach dislocation are termed major subluxation. Major subluxation can be brought on by strenuous activity although it often occurs even in the absence of such activity. Recurrent patellar subluxation both major and minor, is a relatively frequent condition among women generally and particularly among women athletes.
Most instances of subluxation or dislocation of the patella due to patellar tracking errors are in the lateral direction because biomechanical forces typically bias the patella laterally when the knee is load-bearing. In addition, subluxation or dislocation of the patella due to patellar tracking errors has the greatest risk of occurring when the knee is approaching extension. When the knee ranges between about 30xc2x0 of full extension and full extension, the trochlear groove becomes relatively small and shallow which is conducive to subluxation or dislocation. Functional disorders of the patello-femoral joint are highly undesirable because such disorders may ultimately lead to cartilage damage and arthritis of the knee. Therefore, a recognized need exists for effective preventative or remedial treatment of patello-femoral joint disorders.
It is an object of the present invention to provide a knee orthosis which prevents or remediates functional disorders of the patello-femoral joint including recurrent patellar subluxation or dislocation. More particularly it is an object of the present invention to provide a knee orthosis which reduces the risk of patellar tracking errors by providing the knee with a patellar tracking guide. It is a specific object of the present invention to provide a knee orthosis which applies a patellar tracking guide to the head of the femur laterally or medially adjacent to the patella to reduce the risk of recurrent lateral or medial patellar subluxation or dislocation. It is a further object of the present invention to provide a knee orthosis having a patellar tracking guide which dynamically tensions when the knee approaches the extension position for maximum effect and dynamically relaxes when the knee approaches the flexion position to minimize interference with the function of the knee. It is still a further object of the present invention to provide a knee orthosis having a patellar tracking guide which is dynamically positioned more proximal to the patella when the knee approaches the extension position for maximum effect and is dynamically positioned more distal to the patella when the knee approaches the flexion position to minimize interference with the function of the knee. These objects and others are accomplished in accordance with the invention described hereafter.
The present invention is an orthosis mountable on a knee having a femoral head and patella. The orthosis comprises first upper and lower arms positionable about the knee and a first hinge assembly positioned between the first upper and lower arms at the knee to one side of the patella. The first hinge assembly includes a lower end of the first upper arm, an upper end of the first lower arm and a pivot rotationally engaging the lower and upper ends of the first upper and lower arms, respectively. The first upper and lower arms are rotatable about the pivot to transition between a flexion position and an extension position. The orthosis further comprises second upper and lower arms and a second hinge assembly, which are substantially the same as the first arms and first hinge assembly, but are positioned at the knee to the opposite side of the patella from the first arms and first hinge assembly. A substantially-flexible tubular sleeve is provided to retain the upper and lower arms in relation to the knee. Alternatively, a stiffened upper cuff is provided to retain the upper arms and a stiffened lower cuff is provided to retain the lower arms.
A compression member is positioned at the femoral head adjacent to the patella on the opposite side of the patella from the first hinge assembly. In accordance with one embodiment, the compression member comprises a tracking guide engaging the knee and a compression plate in overlying engagement with the tracking guide. The compression plate is formed from a substantially more rigid material than the relatively pliant tracking guide. A tension strap is connected to the first hinge assembly at a first connection paint by means of a tension strap mount. In accordance with one embodiment, the tension strap mount includes a pivot and a mounting plate. The pivot of the tension strap mount is spatially offset from the pivot of the first hinge assembly and rotatably connects the mounting plate to the lower end of the first upper arm or to the upper end of the first lower arm. The tension strap is additionally connected to the compression member at a second connection point which is on the compression plate.
When the first upper and lower arms rotatably transition from the flexion position to the extension position, the first connection point is posteriorly displaced relative to the hinge pivot to position the compression member more proximal to the patella while increasing the tension force applied to the compression member. Conversely, when the first upper and lower arms rotatably transition from the extension position to the flexion position, the first connection point is anteriorly displaced relative to the hinge pivot to position the compression member more distal to the patella while decreasing the tension force applied to the compression member. The orthosis is further provided with a counterbalance connector connected to the compression member and oriented counter to the tension strap.
The present orthosis enables a method for maintaining proper tracking of the patella relative to the femoral head during range of motion movement of the knee. The method is initiated by placing the compression member in engagement with the knee at a location on the femoral head adjacent to the patella. The compression member is aligned with a desired dynamic patellar track. Range of motion movement is then performed on the knee by moving the knee from a flexion position to an extension position or from an extension position to a flexion position while applying a tension force to the compression member by the tension strap. The tension force is increased and the compression member is drawn closer to the patella when the knee approaches the extension position. Conversely, the tension force is decreased and the compression member is drawn away from the patella when the knee approaches the flexion position. As such, the compression member presses against the femoral head with a variable tension force and is dynamically positioned relative to the patella which enables the compression member to conform the patella to the desired dynamic patellar track during movement of the knee.
The present invention will be further understood from the drawings and the following detailed description.